This invention relates generally to gas turbine engines and, more particularly, to gas turbine power systems configured for use in stationary, ground-based applications.
Gas turbine power systems of this particular kind are commonly used in numerous applications, including the compression of gas and the generation of electrical power. When used as part of a co-generation electrical power plant, such systems typically include a gas turbine engine that rotates a drive shaft coupled to an electrical generator and optionally further include a heat recovery device such as a steam generator that recovers heat from the engine's exhaust stream.
One typical gas turbine power system of this kind is illustrated schematically in FIG. 1. The illustrated system is a "cold-end drive" installation, with its electrical generator mechanically linked to the engine adjacent the engine's low-pressure compressor, where cold air arrives at the engine's intake. More particularly, a gas turbine engine 11 drives a rotary power drive shaft 13 that is connected to an electrical generator 15, to generate electrical power. The engine is driven by a hydrocarbon fuel and air, which is delivered via an inlet duct 17 and fed to the engine's intake 19 around the drive shaft. The engine produces a hot exhaust stream that is directed through an exhaust plane 21 to a heat recovery steam generator 23, where heat is recovered from the exhaust and used to produce additional electrical power. Finally, the exhaust stream exits the system via an exhaust stack 25.
Passage of the exhaust stream through the heat recovery steam generator 23 and the exhaust stack 25 can lead to a pressure loss on the order of 11 to 14 inches of water, or 0.4 to 0.5 pounds per square inch. This, in turn, requires a corresponding positive pressure at the site of the engine's exhaust plane 21. While the gas turbine engine 11 can readily provide the required positive pressure at its exhaust plane, this level of back pressure can impose upon the engine an efficiency or power loss that is typically 2% greater than a gas turbine engine exhausting freely into the atmosphere.
Many parameters affect the output and efficiency of gas turbine power systems, and turbine designers have steadily improved the basic efficiency of such systems, typically using ever-higher combustion temperatures and more efficient internal aerodynamic designs. Some design efforts also have been directed towards reducing the power loss through any downstream device such as a heat recovery steam generator. Such efforts have reduced the engine's back pressure, and thus improved efficiency. It is considered, however, that the back pressure imposed on the engine can be reduced even further.
It should, therefore, be appreciated that the need exists for a stationary gas turbine power System that further improves efficiency, specifically by further reducing the back pressure imposed on the system's gas turbine engine. The present invention satisfies these needs and provides further related advantages.